Preparation of dimethyl tin dichloride by direct reaction



May 25, 1954 E. G. ROCHOW PREPARATION OF' DIMETHYL TIN DICHLORIDE BYDIRECT REACTION Filed May 17, 1951 Patented May 25, 1954 UNITED STATESPREPARATION OF DIMETI-IYL TIN DICHLO- RIDE BY DIRECT REACTION EugeneGeorge Rochow, Winchester,

Mass., as-

signor to Metal & Thermit Corporation, New York, N. Y., a corporation ofNew Jersey Application May 17, 1951, Serial No. 226,914

9 Claims. 1

The present invention relates to the preparation of dimethyl tindichloride.

Dimethyl tin dichloride has been found particularly useful in thepreparation of derivatives serving as stabilizers for chlorinatedorganic materials such as vinyl chloride resins, chlorinated paraffins,etc. and as additives for petroleum. For example, the dimethyl tindichloride may be employed to make dimethyl tin dilaurate by reaction ofthe dichloride with sodium laurate.

It has been determined in accordance with the present invention thatadvantageous yields of dimethyl tin dichloride may be produced by thedirect reaction of molten tin and gaseous methyl chloride undercomparatively high temperatures and moderate pressures. The rate ofreaction is dependent on temperature up to a point where excessivemethyl chloride decomposition sets in. The reaction is desirably carriedout at a temperature of between 300 C. and 450 C. When carrying out thereaction without catalyst, a temperature of about 300 C. has been foundsuitable. For a catalyzed reaction, a temperature of about 350 C. ispreferred.

No high pressure is required for the methyl chloride. Its pressure mustbe such as to allow it to be introduced with the molten tin below itssurface and to bubble up through said tin to said surface. For thatpurpose, a pressure of about 60 pounds per square inch gauge has beenfound suitable.

In carrying out the process of the present invention, the gaseous methylchloride is bubbled through the molten tin in a reactor by a continuousoperation. The eiiiuent gas contains a mixture of the excess unreactedmethyl chloride and the reaction product dimethyl tin dichloride. Thesegases can be separated by condensation. The dimethyl tin dichloridecondenses in a cool portion of the system as elongated colorlesscrystals which melt at 106 C. and boil at 189 C. These crystals aresoluble in water, alcohol, benzene and hexane and can be recrystallizedfrom toluene solution.

It has also been found in accordance with the present invention that thepresence of copper promotes the reaction by its catalytic action. Anadditional trace of zinc is effective to promote catalytically thereaction. About 5 to 10% by weight of copper and .01 to 1% of zinc inthe tin bath facilitate reproducibility and initiation of reaction.

It has also been determined in accordance with the present inventionthat if dimethyl tin dichloride is introduced into the reaction zonedirectly or by saturation of the methyl chloride gas stream, thisdichloride will serve as an autocatalyst in facilitating the initiationof the reaction.

Ithas also been found that the presence of sodium during the reaction isdetrimental and should be avoided. The presence of this metal in thereaction zone causes the formation of trimethyl tin monochloride ratherthan the dimethyl tin dichloride desired.

With the process of the present invention, technical methyl chloridecould be used instead of the more expensive refrigeration gradecontaining less water. Although traces of water in the methyl chloridemight cause the production of hydrochloric acid, this has no adverseeifect on the reaction and on the contrary operates as a catalyst.

Various other features and advantages of the invention will be apparentfrom the following particular description and from an inspection of theaccompanying drawing showing diagrammatically a form of apparatus whichcan be employed to carry out the process of the present invention.

Referring to the drawing, there is provided a reactor I0 which may bemade of glass to avoid corrosion from stannous and cuprous chloridesformed during the reaction. If an iron reactor is used, the metalexposed to the tin-gas interface may require to be lined with a suitableprotective material. A suitable lining material for the purpose Would bean anti-corrosive alloy such for example as Hastelloy containing nickel,3% copper, 11/% aluminum and the rest mainly silicon.

The reactor l0 contains a body Il of molten tin extending up to thelevel A therein and adapted to be introduced into the reactor through apipe i3. The reactor I0 is heated by any suitable means (not shown)regulated automatically through thermostatic means in a well I4extending into the tin bath l I. Immersed' in the tin body Il is aninverted box or case l5 having an inlet connection i6 for the gaseousmethyl chloride gas stream and a top wallr Il with a series of holes I8.An outlet 20 leading from the head chamber of the reactor l0 serves as adischarge for the reaction product dimethyl tin dichloride and for theexcess unreacted methyl chloride. An air condenser (not shown) in theoutlet line 20 condenses the dimethyl tin dichloride in crystallizedform.

In operation, the reactor I0 is preheated and loaded with well-dressedmolten tin through thel thermo-couple pipe at 350-400 C. This loadingoperation is performed under the protective blanket of methyl chlorideor nitrogen. Purging of the apparatus and the tin with hydrogen ornitrogen for a few hours speeds initiation of the reaction. The methylchloride is introduced into the box l at a moderate pressure, as forexample, about 60 pounds per square inch, to create a gas chamber 2|therein above the level of the tin in said box. The gas passes throughthe holes I8 in the box Wall I1 and bubbles through the tin above saidwall into the head chamber of the reactor l0. During the bubblingoperation, a fraction or the methyl chloride reacts with the tin to formmainly dimethyl tin dichloride, a little mono' methyl tin trichlorideand a trace-of'trimethyl tin chloride. This reaction product andtheexcess unreacted methyl chloride gas are discharged through theoutlet to a separation point-as described, where the dimethyl tindichloride is condensed out of the exit gas stream. The exit gas, afterbeing stripped of methyl tin compounds, is virtually unchanged methylchloride which can be recycled.

The following examplesillustrate certain ways in which the principle ofthe invention has been applied but these are not to be construed aslimiting the broader aspects Vof the invention.

Example 1 n A 500 ml. round bottom'o'ask was fitted with a 360 C.thermometer, a 5 mm. gas inlet tube and a 5 mm. outletA tube passinginto a West condenser. Mossy tin, 200 gm. and copper powder, 40 gm. wereplaced the ask. The flask and its contents were heated to 300?A C.Methyl chloride gas was then passed'in at about 25 cc. per minute. Inthe course of 2-21/2 hours, the temperature was raised to 320 C. and thegas flow rate had been increased to about 100 cc./minute. At about thistime, white crystals were noticed in the condenser. The reaction wascontinued for an hour and additional crystals plus some liquid werecondensed in the collection system. The crystalline condensate wasidentified as dimethyl tin dichloride. Y

Eample 2 A glass reactor 50 mm. wide and 200 mm. high was provided witha 6 mm. gas inlet tube, thermometer well and a 20mm. take-oli tube atthe top. It was wrapped with asbestos paper and provided with AaNichrome wire heating coil. This reactor was heated to 250 C. 992 gm. ofmolten Grade A tin, 99.2 gm. of reduced copper and 9.92 gm. ofgranulated zinc were added in that order. The reactor temperature wasa'djusted to 80G-805"V C. Methyl chloride gas was introduced at a rateof '7.5 CCL/min; as indicated on a owrator. In the rst two hours, liquidwas condensed in the air condenser attached to the reactor; Aarter twohours, solid dimethyl tin di chloride was deposited in the condenser. ADry Ice-kerosene cold trap was on the gas exit from the air condenser.The gas flow continued for 20r hours at 7.5 cc./min.fand 28 hours at11.25 cc./min., a total of 62.25 gm. being passed. v7'7 gm.of'crude'dimethyl tin dichloride were collected, corresponding to 35.35gm. of methyl chloride. 28 gm. of methyl chloride were condensed in thecold trap. Thus a complete recovery of excess methyl chloride wasobtained and a 56% conversion of methyl chloride to methyl tin compoundwas shown. Y

The reactor was run for an additional 48 hours at 15 cc./min. methylchloride ow rate. Thev chloride.

Example 3 An 'alliron reactor duplicating in dimensions and design theglassreactor in Example l was kheated to 350 C. It was loaded with 990gm. of molten'QradeLA tin, 99 gm. of reduced copper powder and 9.9 gm.of granulated zinc. The temperature was maintained at 30D-5 C. Methylchloride gas was passed in at a flow rate of 100 col/min. In a 48 hourperiod, 212 gm. of crude dimethyl tin dichloride were collected in acondenser. `A'17.1% vconversion ofmethyl'chloride resulted. 97% ofthemethyl chloride was acfor as either product or useable exit gas.

counted Example 4 A two-liter lglass resin ilask was tted with threegasinlet tubes, a-thermocouple well and a product and'excess gas exit toan air condenser. The flask was* heated to a temperature 'above themelting point of tin. 6.5 kilograms of' Grade A tin were introduced. 34grams of dross were removed. 650 gms. of reduced copper powder and 65gms. of granulated-zinc were added. Hydrogen gas was bubbled through-thereactor for 6l/2 hours. 1.8 grams of water were collected. Immediatelyafter the hydrogen ow was stopped, methyl chloride gas was caused toflow through the three gas' inlet tubes. In ten minutes, crystals ofdimethyl tin dichloride were noted.

The average gas input 4rate was 263 cc./min. About 17%of ythis gas wasconverted to product. About of the methyl chloride'gas was accounted foras either productor excess-methyl chloride. The average `4temperature ofthe reaction was y425" C. Onrunning for 68 days,fll5.4

kilograms of Vcrude -productwere obtained. The reactor was opened `after16 days of operation and some slag was removed. '70% of the tin wasconverted to methyl tin compound. The tin in the residue and slag-wasrecoverable.

Example 5 A resin kettle as described in Example 4 was loaded with '7.94kilograms of well-drossed'Grade A tin while under a hydrogen gasblanket. vThe reactor was completely assembled and the hydrogen wasreplaced by methyl chloride gas. The temperature atv this time was 245C. and the stabilized temperature of reaction was 385 C.

After 11/4 hours, no producthad formed; but therewas, some gray powder(stannous chloride) in the condenser and a black scum onthe surface ofthetin. The reactor `was opened and the-scum was removed. Then, afterreassembling kettle, 1.2` gm.V of vdimethyl tin dichloride were used'to,seed the reaction' by-dumping alittle in each of the three gas inlettubes. This material'was almost immediately recovered inthe condenserand the reaction started.

Dimethyl tin dich'iloride was produced at Ythe rate of 2.9 gm./hr. forthe rstthree' hours. This rate increased to 5.2 grd/hr. for the next 24hours and the increase in rate continued steadily for aboutl 200 hours.At the end of 310 hrs., the re-v actor was producing product at a rateof 13 gni/hr. This work utilized a methyl chloride gas flow rate of 250cc./min. At the end of 310 hrs., no scum had formed on the surface ofthe tin.

What is claimed is:

l. The process of making dimethyl tin dichloride, which comprisesreacting methyl chloride directly with tin containing a trace of Zinc.

2. The process of making dimethyl tin dichloride, which comprisesreacting methyl chloride directly with tin in the presence of copper andzinc in catalytic amounts and in the absence of sodium.

3. The process of making dimethyl tin dichloride, which comprisesreacting methyl chloride directly With molten tin containing 5 to 10%copper by weight and .01 to 1% zinc by Weight.

4. The process of making dimethyl tin dichloride, which comprisesbubbling methyl chloride through molten tin containing copper and zincin catalytic amounts.

5. The process as described in claim 4, the reaction temperature beingmaintained at 300 to 450 C.

6. The process of making dimethyl tin dichloride, which comprisesbubbling gaseous methyl chloride under moderate pressure through a bodyof molten tin at a temperature of 300 to 450 C. containing 5 to 10%copper by weight and .01 to 1% zinc by Weight and in the absence ofsodium.

7. The process of making dimethyl tin dichloride, which comprisescontinuously bubbling methyl chloride through molten tin containingcopper and zinc in catalytic amounts and continuously subjecting theefuent gas to condensing temperature to separate the dimethyl tindichloride from the excess unreacted methyl chloride.

8. The process of making dimethyl tin dichloride, which comprisesbubbling methyl chloride and some dimethyl tin dichloride through moltentin during initial stages and subsequently discontinuing the bubbling ofdimethyl tin chloride through the molten tin.

9. The process of making dimethyl tin dichloride, which comprisescontinuously bubbling gaseous methyl chloride and dimethyl tindichloride through molten tin heated to a temperatre of between 300 and450 C. and containing `5 to 10% by weight of copper and .01 to 1% byweight of zinc, in the absence of sodium, after reaction has beeninitiated at substantial rate, discontinuing the bubbling or" dimethyltin dichloride through the tin and subjecting the eiiluent gas to a lowtemperature to condense the dimethyl tin dichloride from said gas.

References Cited in the file of this patent Krause: Die Chemie derMetal, Organischen Verbindungen, page 337, Edwards Brothers Inc., AnnArbor, Michigan, 1943.

1. THE PROCESS OF MAKING DIMETHYL TIN DICHLORIDE, WHICH COMPRISESREACTING METHYL CHLORIDE DIRECTLY WITH TIN CONTAINING A TRACE OF ZINC.